I'm putting this here as a guide for people who are looking to purchase memory for gaming. It can be used by everyone, but a lot of it is technical in nature, so put on your geek glasses and take a trip down memory (timing) lane with me. I just found out most of this. Maybe everyone already knows all of this. For those who don't though, read and learn!

READ THE SPD (also called the SPD dump) for every single stick or memory you buy or own from now on. Demand a copy of it before you buy it and match it after you install it. NO MATTER WHAT IT SAYS ON THE LABEL!! What is the SPD? The SPD contains information the computer needs to talk successfully to the memory. It allows the memory to self-configure to the processor/motherboard combo. The memory controller uses the information contained in the SPD to adjust itself to the particulars of each stick of memory. Freaky people like me enter the BIOS and adjust these silly things. Overriding the values the SPD provided to give us more performance and/or stability, but can also bring a system to it's knees if adjusted improperly. Thus, the SPD (Serial Presence Detect) contains all the values to provide stable and safe operation under most conditions, without you having to do a thing.

The first thing you need is a program that can read the SPD off the dimm. I use a program called Sandra, written by SiSoftware. It's a fabulous program for those of you who have never heard of it, and for those who have, they already know how awesome it is. You can download the free version from majorgeeks.com or download.com. Just search for “sandra”. Another tool I mention in the article is SPDTool. Nobody should ever download or use this program. You can write directly back out the SPD with this tool and destroy the DIMM. Here is a link to it: http://forums.techpowerup.com/showthread.php?t=20349 :) Sandra is safe because it can only read the SPD, not write to it. Another excellent read-only program is CPU-Z.

After you install Sandra and launch it, look under the hardware tab, there is a selection named “Motherboard”. Double click this. Wait a few seconds for it to search your hardware and open a window with the results in it. Just before halfway down, you should see a section named “Memory Module X”. It will have one of these for every DIMM installed in your machine.

Let's define a few terms before we go any further. Below, you may see timings referred to as 800Mhz, 400Mhz or PC2-6400. They are all equivalent. PC2-5300, 667Mhz and 333Mhz are also equivalent measurements of memory speeds. Why? The actual clock speed piped to the DIMM is the lowest number of the group. 333 and 400MHZ, for example. The DDR and DDR2 rating attached to the name means that it can deliver data on the leading and trailing edge of a clock pulse. Try to think of it as being able to take two turns in a chess game. One play when the clock starts your turn, and another when it ended your turn. This is where the second number comes from. 800Mhz = 400Mhz, but with two memory reads for every clock tick (double data rate, DDR, DDR2), you effectively have the throughput of an 800Mhz clock, without the hassle of an 800Mhz bus. PC-2 6400, 5300, 4200 refer to theoretical maximum throughput for the memory. How much it could deliver if everything were perfect. 8 bytes of data (32 bits for those counting at home. Sound familiar?) is made available to the processor 800 million times a second (800Mhz). 8 bytes X 800 million theoretical opportunities to provide data to the processor give us a maximum theoretical bandwidth of 6,400,000,000 (6.4 billion, or Gigahertz (Ghz) ) bytes per second = the designation PC2-6400. 8 bytes times 667 million theoretical opportunities to provide data to the processor give us a maximum theoretical bandwidth of 5,328,000,000 (5.3 billion, or Gigahertz (Ghz) ) bytes per second = the designation PC2-5300.

Phew! Ok lets move on now.

Let's start off with the DIMM's in my machine as I type this article. They are from a major manufacturer. On the label in the picture at the top of this article it says “PC2 6400 Dual Ch Platinum Revision 2 4-4-4-15”* I put them under the microscope with Sandra and I could not believe my eyes!

Memory Module 1
Model : OCZ2P800R21G
Serial Number : 4F435A32
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-15 (tCL-tRCD-tRP-tRAS)
Version : 2.3
Date of Manufacture : Sunday, September 17, 2006
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-15 (tCL-tRCD-tRP-tRAS)
Set Timing @ 333MHz : 4.0-4-4-12 (tCL-tRCD-tRP-tRAS)
Set Timing @ 270MHz : 3.0-3-3-10 (tCL-tRCD-tRP-tRAS)

HUH? According to the label, this is supposed to be a 4-4-4-15 set, not a 5-5-5-15 set! Even if they were mistaken and used the 333Mhz timings, why is the RAS 15 instead of 12? Ugh.

So, even though the label says 4-4-4-15, the SPD says something entirely different. Certainly not what I thought I bought!

Cool to note also, is the date of manufacture. Day before my son's birthday last year, these were rollin' off the production line in Taiwan, only to end up in my grubby little paws a few months later and into my computer a few seconds after that......(in my best Mr. Burns voice, while tapping my finger tips together) “Ehhhhhxcelent”


Next, lets look at a the Patriot 2GB DDR Dual channel set (P/N PDC22G6400LLK). Again, a major manufacturer, known for performance, value and reliability. The only timings marked on the outside of the package are 4-4-4-12. It's what follows that is the gotcha. 2.2v! Anyway, here's the SPD dump from one of the pair.

Memory Module 1
Model : PDC22G6400LLK
Extended Information : mVNP 3
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-16 (tCL-tRCD-tRP-tRAS)
Version : 1.2
Date of Manufacture : Saturday, December 25, 1999
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-16 (tCL-tRCD-tRP-tRAS)
Set Timing @ 267MHz : 4.0-3-3-10 (tCL-tRCD-tRP-tRAS)
Set Timing @ 200MHz : 3.0-3-3-8 (tCL-tRCD-tRP-tRAS)
Enhanced Performance Profiles : Yes
Profile @ 400MHz: Optimal : 4-4-4-12 (tCL-tRCD-tRP-tRAS) CR2 5.0V

OK, again, let me repeat, HUH? 5-5-5-16? Are you kidding? Where does it say that!? Look at the timing profiles too. 400Mhz, 267(???)Mhz, 200Mhz. I thought there was supposed to be a set of timings for 333Mhz? Is this not compatible with systems needing PC2-5300 memory? 200Mhz!! For what? My Duron? My Celeron?

Another very revealing line is the date of manufacture. To think that they have had this density of memory since Christmas Day, 1999? Those royal jerks!

Another conclusion that you could “jump” to is that all the information in the SPD is junk. Yet another conclusion is that Sandra is providing me with incorrect results. So, I fired up SPDTool v0.62 and it gave me the same results as Sandra. Blah.

The last line of the SPD dump gives us hope! OK here is our 4-4-4-12 @ 400Mhz timings!! Yay!! Wait, what's this about 5.0V though? Well, If we put this together with the 2.2v on the outside of the box, we can pretty much determine that in order to get the 4-4-4-12 timings, you have to bump up the voltage to 2.2v! A 20% increase over standard voltage of 1.8v!! That's only if your motherboard can provide that voltage to the socket. If not, you could try and change the timings without adjusting the voltage, but that is risky too. Increasing the voltage increases the Signal to Noise ratio. This is why geeks who overclock crank up the voltage. The increase in S/N ratio allows the memory to provide the data to the memory controller relaibly by increasing the difference between what is considered “on”, the “1” or “high” voltage and the “off”, “0” or “low” voltage. The increase in voltage is accompanied by an increase in heat. The increase in voltage adds to stability, as long as the heat is properly dissipated.

A 20% increase in voltage and probably heat as well. Need a memory cooler? Not only that, but you will probably have to get a program like SPDTool to READ the timings and set them correctly in the bios yourself.

To Patriot's credit, it does say in the flyer included that “...you may have to alter the DRAM timings and voltage settings in your computer bios to reach published performance marks.”

Hmmmm...


Well, I'd like to end this by showing you the SPD from some generic DIMM's i got. The company that produced them is named Adata (www.adata.com.tw). I've been selling them as mid-level gaming and overclockable dimms with average timing specs, and a fantastic price based on the information I could find from them. Let's look at the SPD and see what it tells us about these Taiwan Treasures.

Memory Module 1
Model : HYQVE1A16
Extended Information : RMP-7A0261
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-18 (tCL-tRCD-tRP-tRAS)
Version : 1.2
Date of Manufacture : Monday, October 15, 2007
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-18 (tCL-tRCD-tRP-tRAS)
Set Timing @ 267MHz : 4.0-3-3-12 (tCL-tRCD-tRP-tRAS)
Set Timing @ 200MHz : 3.0-3-3-9 (tCL-tRCD-tRP-tRAS)

Looks like they are made of Hynix chips. All timings are reasonable. Nothing to great, but very acceptable. Definitely worth the money. I was honestly afraid I was going to read the SPD and it would say something like “10-10-10-50”. But for as close as they are to the actual speeds of the name brands, the difference in price more than makes up for the slight difference in timing.

There will always be purists who will demand the “chateau brion” of memory. The 3-3-3-9 timing @ 400Mhz, 1.7v, single sided, self cooling DIMM with heatspreaders made from virgin copper and silver, imported daily, directly from the energy vortexes and copper mines near Jerome / Sedona, Arizona. From what I have seen, I would even check them to make sure they are what they say they are.

If I had my way, I would call on all sellers to post the entire contents of the SPD from the DIMM they are selling, or from a representative sample, selected directly from the batch they are selling. This might mean that some buyers would get opened packages while paying full price, as they get the sample selected to produce the SPD dump. Since manufacturers do not currently provide this to us, I think it the benefit would outweigh the drawbacks for any reputable seller. I think too, that as long as sellers do not take advantage of this practice, the end user is still guaranteed the full manufacturer's warranty, and a reasonable explanation is provided why this particular package is opened, most buyers will accept it. This should only be a short term fix too. Hopefully, manufacturers and distributors will hear us raise our voices on this topic and address it in some fashion. Like posting guaranteed minimum timing values at standard voltages and standard speeds on the package, or included somewhere in the product description, so we can compare them to what we actually get when we install them in our machines.

So, once again, Here is what Sandra said about the three samples I used while writing this article:

Memory Module 1
Model : OCZ2P800R21G
Serial Number : 4F435A32
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-15 (tCL-tRCD-tRP-tRAS)
Version : 2.3
Date of Manufacture : Sunday, September 17, 2006
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-15 (tCL-tRCD-tRP-tRAS)
Set Timing @ 333MHz : 4.0-4-4-12 (tCL-tRCD-tRP-tRAS)
Set Timing @ 270MHz : 3.0-3-3-10 (tCL-tRCD-tRP-tRAS)

Memory Module 3
Model : HYQVE1A16
Extended Information : RMP-7A0261
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-18 (tCL-tRCD-tRP-tRAS)
Version : 1.2
Date of Manufacture : Monday, October 15, 2007
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-18 (tCL-tRCD-tRP-tRAS)
Set Timing @ 267MHz : 4.0-3-3-12 (tCL-tRCD-tRP-tRAS)
Set Timing @ 200MHz : 3.0-3-3-9 (tCL-tRCD-tRP-tRAS)

Memory Module 4
Model : PDC22G6400LLK
Extended Information : mVNP 3
Type : 1GB DIMM DDR2-SDRAM
Technology : 16x(64Mx8)
Speed : PC2-6400U DDR2-400
Standard Timings : 5.0-5-5-16 (tCL-tRCD-tRP-tRAS)
Version : 1.2
Date of Manufacture : Saturday, December 25, 1999
Memory DC Line : 1.8V
Set Timing @ 400MHz : 5.0-5-5-16 (tCL-tRCD-tRP-tRAS)
Set Timing @ 267MHz : 4.0-3-3-10 (tCL-tRCD-tRP-tRAS)
Set Timing @ 200MHz : 3.0-3-3-8 (tCL-tRCD-tRP-tRAS)
Enhanced Performance Profiles : Yes
Profile @ 400MHz: Optimal : 4-4-4-12 (tCL-tRCD-tRP-tRAS) CR2 5.0V

I purposely left out Memory Module 2, because it is exactly the same as Module 1.

Here is what CPU-Z tells us:



Matches Sandra. Now onto the Adata memory



Matches Sandra again. Finally, the Patriot RAM



Obviously, CPU-z does a better job of handling the extended information than Sandra. You can actually see the fourth column has an EPP or Enhanced Performance Profile which clearly states that in order to get 4-4-4-12 timings, you have to crank up the voltage to 2.2v, which is not what Sandra showed us. It's always good to double check your results with another program before you determine that the world has come to an end.


I would love to hear from you and hear your experiences and opinions on this topic. Download one of the three programs above (or use your favorite and teach me something new) and check the DIMMs installed in your machine right now. Are the timings what you thought they were? Are they what you paid for? Send me your SPD dump along with what you were expecting and after I get enough of them, I will start a list of the SPD dumps so anyone can look them up by part number for free before they buy anything.

Send me a message and let me know. Are there technical errors or omissions? Let me know too. I'll make the needed corrections ASAP. If you are a manufacturer and feel your product has been misrepresented here, please contact me, tell me what I am doing wrong and how to fix it and I will include it here as well, or make the needed corrections to this guide.

Find this guide useful? Boring? Pretentious? Over-Rated? Deity-like? Send me a message here on ebay. Tell me what you think, or add to my list of SPD dumps to help prevent other sellers from having to open the package.

All props to SiSoft for writing Sandra, to the folks who made CPU-Z and SPDTool, much thanks as well.  And of course, the memory manufacturers, without whom, none of this would be possible.

az computer g33k


*I hand made the CPU water cooling block in that pic myself and I think it is TONS better than one you can buy commercially today. If you are a reviewer or a company and would like one to test, and are willing to sign a non-disclosure, non-compete agreement, and dont mind the garage, grunge look, contact me directly and I will make one for you.